The present invention relates to a liquid crystal display device, and more particularly to a technique which is effectively applicable to drive circuits of a liquid crystal display device used in a portable display device.
Liquid crystal display devices of STN (Super Twisted Nematic) type or of TFT (Thin Film Transistor) type have been popularly used as display devices of notebook type personal computers or the like. The liquid crystal display device includes a liquid crystal display panel and drive circuits for driving the liquid crystal display panel.
Among these liquid crystal display devices, the number of liquid crystal display devices which are used as display devices of portable terminal devices such as mobile telephones or the like is increasing. To use the liquid crystal display devices as the display devices of the portable terminal devices, further miniaturization and high definition are requested compared to conventional liquid crystal display devices.
As the liquid crystal display device which can realize the miniaturization and the high definition, there has been known a liquid crystal display device which uses polysilicon TFTs as switching elements and forms drive circuits on a substrate on which pixel electrodes are also formed (hereinafter referred to as “drive circuit integral type liquid crystal display device”)
In the display devices of the portable terminal devices such as the mobile telephones, along with spreading of electronic mails attached with images, further enhancement of image display functions such as high image quality, high definition and the like is demanded. Further, in view of the nature of these display devices that they are used as the portable terminals, further low power consumption is also demanded. Still further, it is also a crucial task of the display devices which are used as the portable terminals to strengthen the competitiveness in cost.
As a problem which arises along with the miniaturization of the portable terminal device, the decrease of a space for mounting drive circuits of the liquid crystal display device is named. Further, with respect to a method for mounting the drive circuits, there has been a demand for so-called screen centering, that is, an arranging method in which a center line of the device and the center of a display screen are superposed to each other. This screen centering restricts positions where drive circuits are mounted and hence, it is necessary to pay sufficient consideration to the arrangement of the display devices. Further, in the conventional liquid crystal display device, although the drive circuits have been arranged at two neighboring sides of the display screen, there is a demand for mounting the drive circuits only at one side, that is, so-called three-side-free mounting. Further, it is also necessary to decrease the number of mounting parts for decreasing mounting areas as well as for lowering a manufacturing cost.
Seeking of the high definition in the miniaturized display device arises a problem that a pitch per one pixel is small and hence, numerical aperture of each pixel is reduced. Further, when the number of pixels is increased along with the increase of a screen size, there arises a problem that the performance of the drive circuits cannot follow a driving speed or a problem that a circuit size is increased and a pull-around length of wiring for signal and power source is increased and hence, the distortion of signal waveforms and the influence of noises cannot be ignored.